The present invention relates to the field of vehicle propulsion systems. More particularly, the invention relates to a hydrostatic vehicle propulsion system consisting of a single, variable fluid displacement pump in conjunction with multiple variable fluid displacement motors, and a motor displacement controller to provide steer-assist and anti-spin functions.
Hydrostatic vehicle propulsion systems frequently are configured utilizing a single variable fluid displacement pump in conjunction with multiple variable fluid displacement motors. Such propel system designs have proven to be quite useful for vehicles that are not adapted particularly well for mechanical transmission and axle configurations. Harvesting machines, for example, often require remote engine location, or unique structural configuration to accommodate processing mechanisms for gathering, feeding and separating crop materials. In such instances, the use of multiple hydrostatic drives that can be located independently at drive wheel locations is quite advantageous.
The use of multiple variable fluid displacement motors connected in a parallel circuit with a single variable fluid displacement pump creates several problems. One problem is maintaining the proper balance of motor torque when the vehicle is being steered through a turning maneuver. Another problem is control of motor torque in a manner that will prevent wheel slip or spin in the event that one or more wheels may lose traction.
It is a primary objective of this invention to provide a vehicle propulsion system comprised of a single variable fluid displacement pump connected in a parallel hydrostatic circuit with multiple variable fluid displacement motors.
Further, it is an objective of this invention to provide a control system that will adjust the fluid displacement of the motors commensurate with the associated relationship of the vehicle steering geometry.
Additionally, it is an objective of this invention to determine the steering geometry of the vehicle by measuring the steering angle of each wheel.
Yet another objective of this invention is to control the fluid displacement of the motors in a manner to prevent wheel spin.
It is also an objective of this invention to measure the rotational speed of each wheel in combination with the steering angle of each wheel to determine and subsequently control the appropriate fluid displacement of each motor to assist steering and prevent wheel spin.